Allyloxy activated surface coatings

ABSTRACT

Allyolxy activated surface coatings of free radical-polymerizable compounds having fugitive acid stabilized metal drier and peroxide free radical initiator form durable films over urethane substrates.

This invention relates to allyloxy activated surface coatings of freeradical-polymerizable compounds, especially to such coatings cured withmetal drier catalysts that are stabilized by strong fugitive acid.

Surface coatings of free radical-polymerizable compounds are preferablycured with an activator or crosslinker to provide a durable coating aswell as with metal drier catalyst, e.g. a cobalt compound, andfree-radical intiator, e.g. a peroxide. A disadvantage of such coatingsis that compositions comprising cobalt compounds as metal drier catalystand peroxide as free radical inititor typically have an undesirablyshort pot life, e.g. often less than about an hour or so. Extended potlife, e.g. at least about eight hours or more, has been provided withcoating compositions comprising a temporary catalyst inhibitor, forinstance acetoxime. Such acetoxime-stabilized coating compositions aresuitable for some applications, however, they often fail to cure, e.g.when applied to urethane substrates.

SUMMARY OF THE INVENTION

It has been discovered that such coating compositions will cure overurethane substrates when the acetoxime stabilizer is replaced with astrong fugitive acid, such as trifluoroacetic acid. Accordingly, aninvention disclosed herein relates to coating compositions comprising:(a) free radical polymerizable compounds, allyloxy compounds, metaldrier catalyst, peroxide free radical initiator and a strong, fugitiveacid as a catalyst stabilizer. Also disclosed are methods of coatingurethane substrates with cured films of such coating compositions.

DETAILED DESCRIPTION OF THE INVENTION

The coating compositions and methods of the invention comprise metaldrier than is effective in catalyzing free-radical polymerization ofunsaturated compounds where the catalytic effect of the metal compoundis reversibly inhibited by a strong, fugitive acid, such astrifluoroacetic acid or other acid having substantially similarproperties of strength, volatility and miscibility with coating systemcomponents. The metal compound can include any of the metal driers whichare well known in the coating industry. Preferred metal compoundsinclude cobalt or manganese compounds, e.g. fatty acid salts of suchmetals. In preferred embodiments the cobalt compound can comprise any ofvariety of compounds such as cobaltous acetate, citrate,acetyl-acetonate, 2-ethyl hexanoate and the like.

In characterizing the acid useful in the coating compositions andmethods of this invention, the term "fugitive" describes the transcienceof the acid under coating conditions. For instance, desirable acids area generally stable component of such metal driers or coatingcompositions providing inhibition of the catalytic action of the metaldrier during storage and application prior to curign conditions.However, when films of such coating compositions are subjected to curingconditions, e.g. elevated temperatures or reduced vapor pressure, theinhibiting effect of the acid is diminished. The transcience of suchfugitive acid can be due to evaporation, e.g. for acids having lowboiling points, or from decomposition, e.g. for acids of low stabilityat elevated temperatures, or from other phenomena tending to neutralizethe inhibiting effect of the acid on the metal drier catalyst.

In many cases preferred acids are carboxylic acids having boiling pointslower than cure temperatures of the coating systems, e.g. acids havingboiling points less than about 300° C., say about 150° C., in many casesmore preferably less than about 120° C. In this regard such a preferredacid is trifluoroacetic acid, having a boiling point of about 72° C.

In other cases preferred acids will tend to decompose into volatilecomponents at temperatures lower than the cure temperature. Suchdecomposing acids can comprise carboxylic acid such as glycolic acid ormineral acid such as hydrochloric acid.

The amount of acid is preferably the greater of an amount sufficient tomaterially retard the catalytic effect of the metal compound at least atstorage conditions of coating compositions. In general higher levels ofacid (e.g. up to about 20, or even 50 times the amount of metal on aweight basis) can be tolerated and may be desired to assure sufficientcatalytic retardation. In some cases it is useful to provide the acid atleast about the equivalent amount of metal compound.

Metal compounds are often provided in coating compositions at catalyticlevels of from about 0.001 to about 1.0% by weight; the acid can beprovided at levels from about 0.01 to about 10% by weight.

Acid-stabilized metal drier can be provided as a solution or suspensionof metal compound in the acid, e.g. trifluoroacetic acid, alone or withother commonly used solvents including water, ketones such as methylisobutyl ketone, methyl ethyl ketone, acetone and the like and mixturesthereof.

The effect of the strong acid is generally advantageously promoted bythe presence of at least a minor amount of water to promote hydration ofthe acidic proton. Since water is often present in minor but sufficientamounts in components used in the driers and coating compositions ofthis invention the deliberate addition of specific quantities of wateris often not required.

The compositions and methods also utilize a free radical initiator. Suchfree radical initiator can comprise peroxides such as t-butylhydroperoxide, cumene peroxide, methyl ethyl ketone provide, lauroylperoxide, benzoyl peroxide, azo-bis(isobutyronitrile) and the like andmixtures thereof.

The free radical-polymerizable compound useful in the compositions andmethods of this invention can be an unsaturated monomer or oligomer ormixture of monomers and oligomers. The nature of the compound is notcritical so long as it is activated towards free radical polymerizationvia the double bonds when it is brought into reactive admixture with ametal drier and/or free-radical initiator. Such compounds include dryingoils such as castor, linseed, oticica, safflower, soybean, sunflower,tung and certain fish oils; acrylic monomers; vinyl monomers such asstyrenic monomers, vinyl ethers, vinyl esters, vinyl imides, vinylamides; maleates and fumarates. In many cases it is preferred that suchcompounds be selected from acrylyl monomers or oligomers; such preferredcompounds desirably having a number average molecular weight less thanabout 4000 and contain from 1 to about 10 unsaturated groups permolecule. A particularly preferred group of acrylyl monomers isrepresented by the structure: ##STR1## where R₁ is selected from thegroup consisting of H, CH₃ and C₂ H₅, where r is an integer in the rangeof 1 to 10 and Z is a saturated or ethylenically unsaturated residue ofan alcohol or polyol, a carboxylic acid or poly carboxylic acid, anamine or a polyamine, an epoxide or polyepoxide or an isocyanate orpolyisocyanate of a number average molecular weight less than about 4000containing a hydrocarbon, ester, amide, ether of urethane backbone. Suchmonomers may be obtained by reaction of acryloyl, methacryloyl orethacryloyl chloride with an alcohol, a polyol, an amine, or a polyamineor by the reaction of acrylic acid, methacrylic acid or ethacrylic acidwith an epoxide, a polyepoxide, an isocyanate, or a polyisocyanate, orby reaction of a hydroxyalkyl acrylate, methacrylate or ethacrylate witha carboxylic acid, polycarboxylic acid, an epoxide, a polyepoxide, anisocyanate, or a polyisocyanate. Such monomers include methyl acrylate,methyl methacrylate, butyl acrylate, 1,3-butylene glycol diacrylate,1,6-hexanediol diacrylate, the polyacrylates, polymethacrylates andpolyethacrylates of polyethylene glycols and polyols, polypropyleneglycols and polyols and poly(tetramethylene glycols) andpoly(tetramethylene) polyols of molecular weight in the range of 100 to4000, pentaerythritol tetracrylate, trimethylolpropane triacrylate,dipentaerythritol monohydroxypentacrylate, ethoxylated bisphenol Adimethacrylate, the diacrylates, dimethacrylates and diethacrylates ofepoxy compounds formed from bisphenol A and epichlorohydrin of molecularweight in the range of 200 to 400, and the polyacryloyl monomersprepared by reacting isocyanate capped polyethers and isocyanate cappedpolyesters of molecular weight up to 4000 with hydroxyethyl acrylate.

The coating compositions and methods of this invention also comprise anallyloxy compound which may tend to activate the cure process. Certainallyloxy compounds can advantageously serve as crosslinking agents toprovide desirable cured film properties. Suitable allyloxy compounds areselected from β,γ-unsaturated ethers having at least one α-hydrogen atomin which the allyloxy group may be represented by the following formula:##STR2## The β,γ-unsaturated ether compound has an equivalency less thanabout 300, based upon the number of β,γ-unsaturated ether groups havingan α-hydrogen, a molecular weight less than about 10,000, and has from 1to 60 β,γ-unsaturated ether groups.

The allyloxy compounds are generally aliphatic in character.Alternatively, compounds having β,γ-unsaturation with a triple bond asin propargyl methyl ether, dipropargyl ether, tripropargyl trimethylolpropane, or hexapropargyl sorbitol may be used and are consideredequivalent to allyloxy compounds for purposes of this invention.Exemplary of allyloxy compounds useful in the compositions of thisinvention are the following: methyl allyl ether, methyl methallyl ether,butyl allyl ether, diallyl ether, allyl methallyl ether, dicrotyl etherdi-(2-chloro-2-propenyl) ether, di-(2-phenyl-2-propenyl) ether,di(1-methyl-2-propenyl) ether, 1-phenyl-2-propenyl ether,di-(3-phenyl-2-propenyl) ether, di-(2-isopropyl-2-propenyl) ether,1,4-diallyl oxy-2-butene, 1,4-diallyloxy-2-butyne, 1,6-diallyloxyhexane, 1,4-dimethallyloxypentane, 2,5-dimethoxy-2,5-dihydrofuran,allyl glycidyl ether; allyloxy compounds prepared from the ionicpolymerization of allyloxyalkyl acrylates, methacrylates, acrylamides orthe allyloxy derivatives of vinyl ethers, such aspoly(allyloxyethylmethacrylate) and poly(allyl vinyl ether); allyloxycompounds wherein the allyloxy group forms part of an oligomericbackbone, such as poly(2-buten-1,4-diol) or 2,5-poly(2,5-dihydrofuran).

Preferred allyloxy compounds may be selected from the group ofpolyethers and polyesters represented by the structural formulae:

    R.sub.2 ((E--.sub.m R.sub.3).sub.n

where R₂ is a radical of molecular weight less than about 10,000obtained by removal of active hydrogen from an active hydrogen compoundselected from the group consisting of water, alcohols, thiols,carboxylic acids, carboxylic amides and amines, where the functionalityof R₂ is n and is in the range of 1 to 10, where E is a divalent radicalselected from the group represented by the formulae ##STR3## and##STR4## where the X groups are independently selected from the groupconsisting of H, CH₃, C₂ H₅ and CH₂ OCH₂ Y, Y being selected from thegroup consisting of CH═CH₂, H₃ C--C═CH₂, and H₅ C₂ --C═CH₂, where a is 0or 1, where R₃ is hydrogen or an unsubstituted or substituted C₁ to C₁₀hydrocarbyl radical, where R₄ is a divalent unsubstituted or substitutedC₂ to C₁₀ hydrocarbyl radical and where the product of m and n is atleast 4 and not more than about 60. It is anticipated that any of thehydrogens in Y, except at least one alpha to the ether group, can bereplaced with a lower alkyl without substantially affecting theinvention and that the resulting compounds would be equivalent to thoseaccording to the invention. Polyethers containing an allyloxy group maybe prepared by ionic polymerization of allyl glycidyl ether or mixturesof allyl glycidyl ether and the appropriate alkylene oxide andpolyesters containing an allyloxy group may be prepared bypolymerization of a suitable dicarboxylic acid and the monoallyl etherof glycerol. Suitable polyesters may also be prepared by substitutingfor the monoallyl ether of glycerol, the monoallyl ether oftrimethylolethane, the monoallylether of trimethylolpropane, themonoallyl ether of pentaerythritol, the diallyl ether of pentaerythritoland similar mono and polyallyl ethers of polyols. Allyl glycidyl etheror methallyl glycidyl ether may also be substituted for the monoallylether of glycerol.

Another group of preferred allyloxy compounds is represented by thestructural formula:

    R.sub.5 (OCH.sub.2 Y).sub.p

where R₅ is a C₂ to C₁₂ aliphatic hydrocarbyl or oxahydrocarbyl radicalof equivalence p in the range of 2 to 12 and Y is a group as definedhereinabove. Such compounds include tetrallyl pentaerythritol, hexaallyldipentaerythritol, hexallyl sorbitol, hexamethallyl mannitol,tetraallyl-β-methyl glucoside, and decaallyl sucrose.

Yet another group of preferred allyloxy compounds are acetals derivedfrom allyl alcohol or methallyl alcohol and aldehydes and those derivedfrom a polyol and an acrolein compound represented by the structuralformulas:

    R.sub.6 (CH(OCH.sub.2 Y).sub.2).sub.q and R.sub.7 (O.sub.2 CHY).sub.r

where R₆ is absent or is a C₁ to C₂₀ unsubstituted or a substitutedhydrocarbyl group, Y is a group as defined hereinabove and q is in therange of 2 to about 30; and where R₇ is a radical of molecular weightless than about 10,000 obtained by removal of at least two activehydrogens from a polyol and r is in the range of about 1 to about 170.Such compounds include 1,1,2,2-tetrakis(allyloxy)ethane,1,1,6,6-tetrakis(allyloxy)hexane and those derived from acrolein,methacrolein or crotonaldehyde and a polyol and those derived frompolyacrolein and acrolein copolymers. Exemplary are triallylidinesorbitol and the polyacrolein acetal of polyvinyl alcohol.

The more preferred allyloxy activator compounds are the polyether andpolyacetal compounds in which the number of allyloxy groups per averagemolecule is in the range of 2 to 40 and the allyloxy equivalent is lessthan about 250. Most preferably the allyloxy equivalent is less thanabout 150.

Depending on the end use and the application requirements it may beconvenient to add any of the other conventional additives for surfacecoating compositions such as solvents, pigments, fillers, reinforcingagents, stabilizers, inhibitors and flow control agents. The proportionsof the ingredients can vary widely depending on the compatibility of themajor ingredients and the nature of the coating to be obtained. Themajor ingredients are advantageously selected to be compatible with oneanother to provide a sufficiently rapid cure of the coating and to avoidimpairment of gloss and clarity of the cured coatings. Compatibility isreadily determined by mixing the major ingredients and determining therange of mixtures which do not form cloudy solutions or coatings orseparate into phases. Provided that the major ingredients are suitablycompatible, a weight range of allyloxy compound tofree-radical-polymerizable compound (e.g. in the range of from 70:30 to1:99) can be used. Preferably this ratio will be in the range from 40:60to 5:95 to provide an adequate rate of cure and an adequate level ofmechanical properties in the cured coating.

In those cases where it may be desirable to provide solvent (or vehicle)for the coating composition of this invention, such solvent ispreferably a volatile organic compound comprising a ketone, such asacetone, methyl ethyl ketone, methyl isobutyl ketone, etc.; an estersuch as ethylene glycol monoethyl ether acetate; an aromatic such astoluene, xylene; or a mixture thereof.

The coating compositions of this invention are advantageously applied asthin films to substrates, most advantageously to urethane substrates,e.g. reaction injection molded (RIM) urethane substrates. Such films aregenerally cured by heating the film, e.g. in an air oven or by IR lamps,to accelerate cure to a tough, solvent-resistant coating. Exposing thefilm to a temperature of at least 50° C. or higher, preferably to atleast 70° C., say about 80° C. provides quite acceptable cured films.Higher temperatures can of course be utilized especially to effectcuring in shorter times.

The following disclosure is provided to illustrate specific embodimentsand aspects of this invention but does not imply any limitation of thescope of the invention.

MATERIALS USED

In the following described materials, the symbol "(n)" indicates asolution in the identified solvent where "n" is the weight percent ofthe described material in solution.

UV1(n): acrylated urethane oligomer obtained from Morton-Thiokol Companyas Uvithane-893, unsaturation 0.15-0.175 equivalents/100 g; diluted withMEK to provide a solution of weight percent indicated in parenthesis,e.g. UVI(75) is 75 wt.%.

AOC: allyloxy compound, a reaction product of ethylene glycol and allylglycidyl ether (1:10 mole ratio) in the presence of borontrifluoride/etherate catalyst at 75°-80° C. The allyl glycidyl ether isadded over a period of 5 hours. The catalyst is neutralized with NaOHsolution. The aqueous phase is separated from an organic phase productwhich is dried and filtered. The liquid organic product has a Gardnerviscosity of F at 25° C. and an allyloxy equivalent of about 120.

MEK: methyl ethyl ketone

BPO: benzoyl peroxide, 10% solution in MEK.

Co(n): a cobalt catalyst compound obtained from Nuodex, Inc. as Nuocure®10% cobalt catalyst in mineral spirits; solution diluted with MEK toweight percent indicated in parenthesis, e.g. Co(0.1) is 0.1 wt.%cobalt.

TFA(n): trifluoroacetic acid in MEK solution where weight percent acidis indicated in parenthesis, e.g. TFA(1) is 1 wt.%.

BYK: a mar and slip additive obtained from Mallinkrodt, Inc. as BYK-341.

ETOH(n): ethanol in water solution where weight percent ethanol isindicated in parenthesis.

EXAMPLE

This example serves to illustrate the effectiveness of substitutingtrifluoroacetic acid for acetoxime as a stabilizer for metal drier incoating compositions comprising acrylated resins and allyloxy initiator.

Compositions, prepared from components indicated in Table 1, wereapplied as thin (about 10 micron thick) films over RIM urethanesubstrates. Composition A stabilized with acetoxime had a suitablyextended pot life; but thin films applied to a RIM urethane substratedid not cure when heated to about 82° C. for 30 minutes. Composition Bstabilized with trifluoroacetic acid had a suitably extened pot life(typically at least about 2 days); and thin films cured to a tack free(to the touch) films when heated to about 82° C. for 30 minutes.Composition B, without peroxide, had exceptionally long pot life (e.g.days); but thin films did not cure.

                  TABLE 1                                                         ______________________________________                                        COATING COMPOSITIONS                                                          (parts by weight)                                                                       Component:                                                                    A          B      C                                                 ______________________________________                                        UVI (75)    5.3          5.3    5.3                                           AOC         1            1      1                                             BPO (10)    1.5          1.5    --                                            TFA (10)    --           0.12   0.12                                          OXI (1)     0.3          --     --                                            MEK         0.19         0.58   0.34                                          Co (.1)     0.5          0.5    0.5                                           BYK         0.06         --     --                                            ETOH (80)   --           --     0.8                                           ______________________________________                                    

While specific embodiments of the invention have been described, itshould be apparent to those skilled in the art that variousmodifications thereof can be made without departing from the true spiritand scope of the invention. Accordingly, it is intended that thefollowing claims cover all such modifications within the full inventiveconcept.

What is claimed is:
 1. A coating composition comprising(a) a freeradical-polymerizable compound, (b) an allyloxy compound, (c) a cobaltdrier catalyst, (d) a peroxide free radical initiator, and (e) a strongfugitive acid as a catalyst stabilizer;wherein said free-radicalpolymerizable compound is of the formula ##STR5## where R₁ is selectedfrom the group consisting of H, CH₃ and C₂ H₅, where r is an integer inthe range of 2 to 10 and Z is a saturated or ethylenically unsaturatedresidue of a polyol, a polycarboxylic acid, a polyamine, a polyepoxideor a polyisocyanate of a number average molecular weight less than about2000 containing a hydrocarbon, polyester, polyamide, polyether orpolyurethane backbone.
 2. A composition according to claim 1 whereinsaid acid comprises trifluoroacetic acid.
 3. A composition according toclaim 1 wherein said allyloxy compound is

    R.sub.2 ((E).sub.m R.sub.3).sub.n, R.sub.5 (OCH.sub.2 Y).sub.p, R.sub.6 (CH(OCH.sub.2 Y).sub.2).sub.q or R.sub.7 (O.sub.2 CHY).sub.r

where R₂ is a radical of molecular weight less than about 10000 obtainedby removal of active hydrogen from an active hydrogen compound selectedfrom the group consisting of water, alcohols, thiols, carboxylic acids,carboxylic amides and amines, where the functionality of R₂ is n and isin the range of 1 to 10, where E is a divalent radical selected from thegroup represented by the formulae ##STR6## where X is selected from thegroup consisting of H, CH₃, C₂ H₅ and CH₂ OCH₂ Y, Y being selected fromthe group consisting of

    CH═CH.sub.2, CH.sub.3 --C═CH.sub.2, and C.sub.2 H.sub.5 --C═CH.sub.2

where a is 0 or 1, where R₃ is hydrogen or an unsubstituted orsubstituted C₁ to C₁₀ hydrocarbyl radical, where R₄ is a divalentunsubstituted or substituted C₂ to C₁₀ hydrocarbyl radical and where theproduct of m and n is at least 4 and not more than about 60: where R₅ isa C₂ to C₁₂ aliphatic hydrocarbyl or oxahydrocarbyl radical ofequivalence p in the range of 2 to 12; where R₆ is absent or is a C₁ toC₂₀ saturated or ethylenically unsaturated residue of a polyol, apolycarboxylic acid, a polyamine, a polyepoxide or a polyisocyanate of anumber average molecular weight less than about 2000 containing ahydrocarbon, polyester, polyamide, polyether or polyurethane backbone.4. The coating composition of claim 1 wherein said film is cured on aurethane substrate.
 5. The coating composition of claim 1 wherein saidfilm is cured on a urethane substrate.